Flowering is an important agronomic trait that determines the planting season and growing area of crops and ultimately affects crop yield．Therefore,adjusting the flowering time of crops is an important way to improve crop yield．In this study,the orthologous gene TaCO9 of the barley(Hordeum vulgare)photoperiod gene HvCO9 in wheat(Triticum aestivum)was obtained by homologous cloning and used as a research object to reveal its function in wheat．Sequence analysis showed that TaCO9 contained 2 exons and 1 intron,the whole length of CDS was 876 bp,291 amino acids were encoded,and the protein sequence contained a unique CCT domain,which was highly conserved among different species．Bioinformatics analysis showed that the molecular weight of the protein encoded by this gene was about 30．7 kD and the pI was 6．24．The prokaryotic expression results showed that the molecular weight of the protein was basically consistent with the predicted results under IPTG induction；PlantCARE predicted that the promoter region of TaCO9 contained many cis-acting elements such as light response,hormone response and stress response；The phylogenetic tree showed that TaCO9 had the closest homology with goat grass and barley,and the sequence similarity was 96．2% and 90．57% respectively．Subcellular localization and transcriptional activity analysis showed that the fusion protein of TaCO9 and EGFP was mainly located in the nucleus,and TaCO9 had transcriptional activation activity．The results of QPCR showed that TaCO9 gene was expressed in all tissues,with the highest expression in leaves；TaCO9 expression level under 14 h light was significantly higher than that under 12 h and 10 h light；and TaCO9 expression level in ovary and grain of XN817 was significantly higher than that under CS．Functional identification showed that the flowering period of transgenic Arabidopsis plants with overexpression of TaCO9 was later than that of wild-type control plants (3-4 d),and the seeds and siliques were larger．This study helps to clarify the function of TaCO9 gene and provides a new theoretical basis for wheat genetic improvement．